1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to wireless communication technology, and more particularly, to efficiently transmitting large multimedia data over a wireless network.
2. Description of the Related Art
As networks become wireless and the demand for large multimedia data transmission increases, there is a need for studies on an effective transmission method in a wireless network environment. In particular, various home devices are increasingly required to wirelessly transmit high-quality videos, such as digital versatile disk (DVD) videos or high definition television (HDTV) videos.
An IEEE 802.15.3c task group is developing a technological standard for transmitting large-volume data over a wireless home network. The technological standard, which is called “millimeter wave (mm Wave),” uses an electric wave having a physical wavelength of a millimeter, i.e., an electric wave having a frequency band of 30-300 GHz to transmit the large-volume data. This frequency band, which is an unlicensed band, has conventionally been used by communication service providers or used for limited purposes, such as observing electric waves or preventing vehicle collision.
FIG. 1 is a diagram comparing frequency bands of the IEEE 802.11 series of standards and mmWave. Referring to FIG. 1, the IEEE 802.11b or IEEE 802.11g standard uses a carrier frequency of 2.4 GHz and has a channel bandwidth of approximately 20 MHz. In addition, the IEEE 802.11a or IEEE 802.11n standard uses a carrier frequency of 5 GHz and has a channel bandwidth of approximately 20 MHz. On the other hand, mmWave uses a carrier frequency of 60 GHz and has a channel bandwidth of approximately 0.5-2.5 GHz. Therefore, it can be understood that mmWave has a much greater carrier frequency and channel bandwidth than the conventional IEEE 802.11 series of standards.
When a high-frequency signal (a mmWave) having a millimeter wavelength is used, a very high transmission rate of several Gbps can be achieved. Since the size of an antenna can also be reduced to less than 1.5 mm, a single chip including the antenna can be implemented. Furthermore, interference between devices can be reduced due to a very high attenuation ratio of the high-frequency signal in the air.
However, the high-frequency signal has a short distance range due to the very high attenuation ratio. In addition, since the high-frequency signal has high directability, it is difficult to have a proper communication in a non-line-of-sight environment. In mmWave, an array antenna having a high gain is used to solve the former problem, and a beam steering method is used to solve the latter problem.
Recently, a method of transmitting uncompressed data using mmWave in a high-frequency band of several tens of GHz has been introduced to home and office environments, along with a related art method of transmitting compressed data using a band of several GHz of the IEEE 802.11 standard series.
Since uncompressed audio and video (AV) data is large-volume data that is not compressed, it can be transmitted only in a high-frequency band of several tens of GHz. Even when having a packet loss, the uncompressed AV data has relatively less effect on the quality of video display than the compressed data. Therefore, there is no need for an automatic repeat request or a retry.
FIG. 2 is a block diagram illustrating a method of transmitting a multimedia stream from a source device to a sink device in a related art wireless home network. Referring to FIG. 2, a source device 21 transmits a multiplexed AV stream to a sink device 22. The source device 21 is a device generating an AV stream from a multimedia source and wirelessly transmitting the AV stream, such as a set-top box, a DVD player, or a portable multimedia player (PMP). The sink device 22 is a device receiving the AV stream and outputting the AV stream in a form that can be audio-visually perceived by a user, such as a beam projector, a television (TV), a monitor, or an AV receiver. Each of the source device 21 and the sink device 22 includes a wireless network interface. From the perspective of a wireless network, the source device 21 operates as a transmitting device, and the sink device 22 operates as a receiving device.
A broad bandwidth is required to transmit large multimedia data such as uncompressed video data, e.g., data that presents red (R), green (G) and blue (B) or yellow-ultraviolet (YUV) components, which constitute a pixel, as digital values. Although the sink device 22 can process only either of a video stream and an audio stream, if the source device 21 transmits an AV stream which contains both audio and video data to the sink device 22, the bandwidth is wasted. Therefore, the source device 21 needs to adaptively transmit a video stream, an audio stream, or an AV stream according to the available capability of the sink device 22.